The Camaro Restoration Handbook (HPBooks-758) has a simplistic explanation, but little in meaty reality.
A good investment would be a RS headlamp diagram which should be available from restoration houses or with a new vacuum line kit.
The 68-69 systems worked marginal at best even when new. Put in a high-performacne motor and it becomes difficult to make them work reliably.
The system consists of the headlight switch, vacuum switch, vacuum tank, rubber lines, and actuators. The actuators are located in front of each front wheel behind a splash guard. The actuators are connected to the RS door hinge assembly. Verify that the door moves freely. If they have never been serviced you may need to clean and lubricate the piviot points or rebuild the assemblies using a bushing kit. The actuators are a pull-on pull-off design, meaning that vacuum is required for both opening and closing. You can test the actuators by applying vacuum to one side of the actuator while plugging the other. If there is a leak, the actuator needs replacement. The vacuum tank, located on the LH front of the engine compartment, rarely goes bad, just check for leaks. The vacuum switch, located on the vacuum tank, controls both vacuum and atmosphere. In order for the actuators to work, vacuum must be applied to one side and the other side must be open (atmospheric). The vacuum switch controls which side of the actuator has vacuum/open. You can test the switch by disconnecting the lines to the actuators, apply vacuum to the system, and move the slide mechanism on top of the vacuum switch to both positions and determine if vacuum is present at both disconnected line locations. In one position vacuum should be present, move the slide and vacuum should be present at the other. The slide mechanism has an o-ring that is not visible that may require replacement. Be very careful moving all of these components since they are usually very fragile after so many years. The slide on the top of the vacuum switch performs the same function as the headlamp switch, alternating between an open and vacuum condition being applied to the vacuum switch. Be sure to check all hoses, tees, and connections for looseness, inluding the engine vacuum line. If you know someone who has a vacuum pump it will make your life a bunch easier.